header part for section titles

[Paul Scott]

If I put a \header in a second \score in a file, 'piece = "II. - 
Whatever"' will print but 'instrument = "II. - Whatever"' does not.  I 
currently use 'piece = ...' to get section or movement names but I would 
like them centered instead of on the left.  Is there a way to get a 
centered section or movement titles for an orchestral/instrumental part 
without using lilypond-book?

                                        Title
                              First Movement (using subtitle or instrument)

music (first movement)....

                                Second Movement

music (second movement)


I see 'instrument' on the left and 'piece' centered more often than the 
reverse but I not really what it's called as long as it works.

TIA,

Paul Scott